Which Foods Are the Most Adulterated? - Identifying Adulteration with Infrared Spectroscopy

Food adulteration is a global problem. Africa Studio | Shutterstock

Food adulteration has been in existence since the Victorian era. Lead salts were used to color cheese, milk and beer was watered down, and ground bones or chalk dust were used to bulk out flour.

Adulteration still occurs due to profit and greed in spite of the stringent quality control processes that governments enforce in an effort to preserve the integrity of food and the negative health effects adulteration can cause.

The problem is widespread in world markets and is highlighted by some sensation cases of food adulteration. In a November 2015 report in the Times of India, the Indian police found that spices are mixed with toxic chemicals such as paint, glue and varnish to make them look more attractive before they are sold to the public. Adulteration greatly affects the confidence of both the public and it affects business.

The 2008 Chinese milk scandal caused melamine poisoning of almost 300,000 babies in China. The Chinese company was prosecuted, and two company executives were executed for their crime. The 2013 horse meat scandal demonstrated that Europe is not out of bounds to food adulteration; and the reputation of many companies was called into question. As a result around 18 million ready meals were thrown away by the public, the market for ready meals collapsed, and public confidence in our food supply plummeted.

Companies have realized that the provenance and integrity of their food supply chain is connected to their reputation in the market, and that they have a public and legal responsibility to guarantee their products are genuine and safe.

For the food industry, Fourier transform infrared (FTIR) spectroscopy is an ideal technique to test the authenticity of produce, due to it's simplicity and it's ability to quickly provide non-destructive measurements.

The import and export of produce worldwide has focused on the provenance and safety of raw materials prior to their use in the production of food items. For many years, FTIR has been used to supplement process and quality control in the food industry, and it is an ideal method to detect food adulteration.

Multivariate data analysis methods and an ease of operation make FTIR a well-suited method to quickly check a large quantity of food produce, as well as to allow the characterization of food components in concentration levels as low as parts per billion.

The Four Most Adulterated Foods

Alcohol, powdered milk, olive oil, and meat products are four of the most commonly adulterated food products.

Alcohol is mixed with ethylene glycol, methanol, or other industrial chemicals, which when ingested can lead to death or blindness. Authorities in Italy and Spain often battle to control olive oil contamination, since extra virgin olive oil is a high-end product, so adulterated cheaper oils are a common occurrence. Milk powder, a common additive in food production, undergoes stringent checks for the presence of fat, protein, and moisture content. Industrial chemicals such as melamine are added to boost the nitrogen levels and fool tests for protein quantitative analysis. Water content in meat is a concern for the food authorities, and strict limits on the amount are imposed to improve texture and flavor.

Alcohol

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Alcohol adulteration is a global problem. Sometimes wine and spirits, especially the low-cost varieties, contain toxic alcohols, industrial dyes, and chemicals such as ammonium nitrate, leading to hundreds of deaths per year. A 2006 Indian study illustrated that 64% of alcohol samples tested positive for methanol content. Ingesting just 30 mL of methanol can be fatal.

Alcohol adulteration can be reliably tested using near infra-red (NIR) spectroscopy with attenuated total reflectance. Strong absorbance is a problem in the mid-IR (MIR) region, the region where the IR chemical fingerprint signals for contaminants are located; this problem can be resolved by the use of ATR and NIR spectroscopy. High accuracy and improvements in the MIR region signals can also be achieved by chemometrics and multivariate analysis.

The presence of adulteration in alcohol samples can be detected using the Pearl™, a liquid transmission accessory for FTIR, produced by Specac. Even if the spirit contains volatile elements, the Pearl’s injection port can provide a definitive analysis.

Olive Oil

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Extra virgin olive oil is a highly demanded, high-value product of Spain, Greece and Italy. To increase profits, some suppliers adulterate oil with low-cost substitutes such as palm oil, peanut oil or even industrial oil.

The 2013 workshop on olive oil authentication held in Madrid provides statistics that illustrate that almost one in three olive oils sampled in Canada, and one in four in Spain failed the fraud tests. The widespread contamination of extra virgin oil has called for stringent tests. The European Union’s Horizon 2020 research program includes a study project on olive oil authentication.

FTIR is an ideal method for oils. It only needs minimal sample preparation, and can identify and quantify adulterants by spotting suspicous functional groups using a fingerprint approach.

An FTIR process performed with attenuated total reflection and multivariate analysis can be used to examine the mixing of peanut oil with extra virgin olive oil. The study analyzed two groups of frequencies to develop a strong regression model, which were from 2,750 to 3,050 cm-1 in the functional group region, and from 600 to 1,800 cm-1 in the fingerprint region. A process was designed to detect contaminant oils at 0.5% v/v levels. The FTIR spectra established that each oil sample has a distinct fingerprint.

The authenticity of olive oil samples in their original state can be proven with the Pearl™. Pearl’s accuracy enables the detection of a chemical fingerprint of low-grade oils at low concentrations. Its design ensures viscous oils can be easily removed after they are measured, avoiding errors in subsequent experiments.

Milk Powder

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Milk powder is a key ingredient in many processed foods. Many cases relating to milk powder adulteration caused by the use of melamine or urea to increase the nitrogen content have been witnessed in India, China, and Brazil. The Food Safety Standards Authority of India found in 2012 that 70% of milk samples in the country were adulterated.

FTIR is regularly used by food companies to determine fat, moisture, lactose, and protein content for QA/QC and production-line process control. Its use has been expanded to also cover dangerous adulterations. A 2011 study demonstrated that FTIR spectra of the MIR region between 4000 and 600 cm-1 can be used to detect if any melamine is present and its concentration. Regression and multivariate analysis can be employed to process the FTIR data. Spectral changes in the finger print region (1800 and 700 cm-1) and amide I and II regions (1700–1400 cm-1) can be used to identify and quantify adulteration, and offer a model for subsequent analysis.

The Quest™ ATR accessory can be used to accurately analyze adulteration in milk samples. The Quest™ enables high throughput quality control as no sample preparation is required.

Meat

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The addition of water to meat is controversial, though EU regulations permit significant water additions. Chicken is allowed a water content of 7% and ham is allowed a water content of 25%. However, the water content is often more than these limits. Prepared and canned meats usually contain a lot of hydrolysed protein, salt, polyphosphates, dextrose or lactose; all of these compounds contain water. Some prepared meat samples have been found to contain just 54% meat, with water, starch and gelatin making up the balance.

In 2000, the FSA found that a third of chickens sold in supermarkets had more than 7% water, with some samples having a water content as high as 37%.

In 2014, a Chinese research team developed a qualitative model to distinguish gum-injected and water-injected meat from normal varieties. Using NIR, discriminant analysis and principal component analysis, the accuracy levels to differentiate adulterated and normal meat varieties was 94.23% for a water-injection level of 1.25%-20%. The accuracy reached 96.96% for water injection levels of 3.75%- 20%.

Solid samples, including cut pieces of meat, can also be tested by the Quest™. This approach allows characteristic wavelengths of water to be identified and quantified with little damage to the food product. This form non-destructive testing is well-suited for food quality control.

The Pearl™

The Pearl™ is a liquid transmission accessory that is used for FTIR sample analysis in the NIR and MIR ranges. Using the Pearl™ considerably reduces the difficulty and time needed for liquid sample analysis. Excellent sample access and easy cleaning between analyses is ensured by the use of the device's Oyster™Lift and Tilt cell assembly.

The Oyster™cell possesses an injection port to enable the analysis of volatile samples. The Pearl™ provides a more accurate path length, compared to conventional transmission accessories; path lengths can be repeatable to within 1 µm.

The Pearl™ can be fitted with CaF2 or ZnSe windows that are quickly interchangeable. The Oyster™cells are available in various path lengths of 50, 100, 200, 500 and 1000 µm.

The advantages of the Pearl™ include:

  • Enables easy FTIR sampling
  • More reliable and quicker than conventional liquid cells
  • Repeatable and accurate path lengths
  • Easy handling of viscous materials such as oils
  • Available as wedged or parallel cells

Conclusion

A traditional ATR IR, combined with the Pearl’s accuracy in liquid transmission, can be used to detect food adulteration irrespective of if the sample is a solid, a powder, an aqueous solution, or an oil. Its ease of use, along with FT-IR processing software, means that only a low level of skill is needed to use the device.

This information has been sourced, reviewed and adapted from materials provided by Specac.

For more information on this source, please visit Specac.

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